The fundamental form of Hon shu, the main island, is outlined by two great mountain systems, which are called the northern and the southern arc. The two systems meet in the central part of the island forming a syn taxis or where lies the great volcanic chain of Fuji. The northern arc, which is often called the Sakhalin system, is quite a large system and consists of several parallel ranges whose northern extension passes through Hokushu, the main island of Hokkaido, to Karafuto (Sakhalin). These ranges run nearly north and south but their southern por tion gradually tends to the southwest. In the northern half of Honshu or northern Japan there are three ranges, separated from each other very distinctly by depressions of low plains. The central range begins on the shore of the Gulf of Mutsu. It runs south, forming the backbone of northern Japan as well as the watershed between the Pacific Ocean and the Sea of Japan. Geologically the range shows the later formations of the Tertiary Period, accompanying a few exposures of Archwan and Palaeozoic formation. Moreover, this range is a series of volcanic cones, forming the Nasu volcanic chain. Some of the cones exceed 7,000 feet in altitude. At the northern extremity of the Nasu volcanic chain stands Osore-yama (2,572 feet) on the north coast of the Gulf of Mutsu. The chain runs south through such volcanoes as Yatsukoda-san (5,153 feet), Ganju-san (6,790 feet), a gigan tic volcanic cone of North Japan, Koma-ga take (3,834 feet), Sukawa-dake (5,435 feet), Zao-san (6,442 feet), Adataro-san (4,658 feet), Adzuma-yama (6,294 feet), Bandai-san (6,442 feet), Nasu-san (6,271 feet), and turns to the southwest and then west through Takahara yama (5,881 feet), Nantai-zan (8.144 feet), the principal peak of the Nikko Group, Hiuchi dake (7,813 feet), Akanagi-yama (7,511 feet), Nikko Shirane (7,504 feet), Akagi-san (6,209 feet), Haruna-san (4,779 feet) and Asama yama (8,134 feet). Some of these are still active. The great eruption of Asama-yama in 1783 and the explosion of Bandai-san in 1888 were most remarkable.
The second range, which runs parallel to the central range and along the coast of the Sea of Japan, is of similar geological forma tion to the first. These ranges are separated from each other by a series of low lands such as the valleys of the sister rivers Omono and Mogami, the basins of Yonezawa, Aidzu and Inawashiro, etc. The range is divided into two parts by the gorge of Mogami. The north ern half, which is composed mostly of hills or low tablelands, is generally comprised under the name of Dewa-hill. The southern half is very mountainous and is called the Echigo Mountain Range. Asahi-dake (7,032 feet) and Iide-san (6,232 feet) are the prominent peaks of the granite mass in this range. The south ern prolongation of the range stretches between the Aidzu basin and Echigo plain and termi nates in Mikuni Range.
A volcanic chain runs parallel to this west ern range. Commencing at Iwaki-san (5,209 feet), it passes through Moriyoshi-yama (4,769 feet), Chokai-zan (6,964 feet) and Gassan (5,944 feet). Chokai is well known because of its gigantic proportions and therefore this chain takes the name of this volcano. The coastal line of the Sea of Japan is mostly flat and unbroken. Its monotony is disturbed only by the volcanic peninsula of Oga, which en closes the shallow waters of the lagoon Hachi ro-gata. The plain of Echigo on the same
coast is one of the largest plains in the country The third range running along the Pacific Coast east of the central range differs from the other two in several respects. It consists of such older geologic formations as Archaean, Palaeozoic and Mesozoic, associated with vari ous kinds of old eruptive rocks. Topographi cally it forms no continuous chain as does the central range, and it is divided into the two spindle-shaped mountain groups, Kitakami and Abukuma. The Kitakami group on the north is sharply separated from the central range by the tectonic valleys of Mabechi and Kita kami. Its external features show no regularity as a mountain system, which can be observed merely in its inner stratified structure. The network of numerous valleys extending in various directions, which have resulted from erosion, divide the district into an irregular group of mountains and hills. Hayachine, the highest peak, measures about 6,560 feet. The coast of this region is not so smooth and flat as the coast of the Sea of Japan, but it is in many places very deeply indented with numerous small inlets of the type, such as Miyako, Kamaishi, Onagawa, etc., afford ing vessels protected anchorages. Near Oshika Peninsula on the south, separated from the mainland by a narrow passage of water, is the granitic island of Kinkazan, whose lofty peak is the sailor's landmark. Waveworn Matsu shima, a group of a hundred small islands in the Bay of Sendai to the west of Oshika Penin sula, is noted for its beautiful scenery.
Another mountainous region, lying between the Pacific Ocean and the tectonic valley of Abukuma, is commonly called the Abukuma Plateau. This is a broad mountain mass, and consists of an extensive area of gneiss and crystalline schists with a narrow zone of coal bearing strata of Tertiary formation along the coast. The abrasion was much greater here than in the Kitakami Mountainland. The An cient mountain system with its complex strata is now reduced to an undulating plateau, whose greatest elevation scarcely exceeds 3,300 feet. The southern extension of this plateau forms the small ranges of Yamizo and Yalca, which gradually sink into the plain of Kwanto. At the extremity of the latter stands an isolated mountain called Tsukuba-san (2,850 feet) • on one of its summits the well-known meteorologi cal observatory was established some years ago by H. I. H. Prince Yamashina. Another extension of the northern arc toward the south west forms the mountain blocks or aSchollea of Ashio and Kwanto or Chichibu, which form the north and northwest boundaries of Kwanto-plain. The Kwanto group is a square mass of the older geological formations. On the west it terminates abruptly in the tectonic valley of Chikuma-gawa and in the basin of Kofu, and on the east in the plain of Kwanto. Some celebrated mountains of this group are Buko-zan (4,297 feet), Kobushi-dake (8,062 feet), and Kimpu-zan (8,367 feet). The great volcanic district of Kenashi and Iwasuge with the extinct volcanoes of the same names lies between the Kwanto group on the south and the Mikuni group on the east. The volcanic chain also stretches to the south until it joins the Nasu volcanic chain at Asama-yama.